Design and Analysis of Slewing Jib Crane - Essay Example

Name: Tutor: Course: Date: Design and Analysis of Slewing Jib Crane Introduction A crane, overhead crane or bridge crane is a machine that is used in lifting, lowering and moving materials in horizontal directions. It is able to lift loads beyond the ability of a human being by use of mechanical advantage created by use of a hoist. At the beginning crane construction made use of wood but during the industrial revolution steel and cast iron replaced wood. Cranes are used for loading or unloading of cargo in transportation activities, in constructions and in the assemblage of equipment in manufacturing industries. For along time the cranes use men and animals as a source of power. Mechanical power was used for the first time in the 18th and 19th centuries from steam engines. “The cranes used in modern times make use of internal combustion engines, hydraulic systems or electric motors.” They have a higher capacity of lifting loads than the cranes used in earlier times. However manual cranes exist and are in use in some places where power is an issue. (Matthies, Andrea 530) There are many types and forms of cranes which are used for different purposes. They vary in sizes from smaller jib cranes available for use in workshops to the tallest ones used in high building construction. Mini cranes can also be used in the construction of tall buildings where there is need to access tight spaces. Bigger floating cranes are useful in salvaging ships sunk in water and building oil rigs (Lancaster 430) Manufacturing plants make use of overhead systems of handling materials. These devices are meant to assist people at work to move objects that weigh between 30 pounds and 100 tons. The figure below shows one of the cranes used called jib crane. The trolley moves on the boom. The load being moved is normally suspended from a trolley by way of a chain and hoist. The jib crane is made with 3 “degrees of freedom” (DOF). The horizontal plane has 2 degrees of freedom which is brought about by the movement of the trolley and boom. The hoist provides the “third vertical degree of freedom” (O’Connor, Colin 49). Figure 1 Typical slewing jib crane Evolution of the crane The first cranes used in construction were discovered by the Greeks in the ancient times. Animals such as donkeys or even men were used as the source of power for the cranes. They were important in tall building construction. This was followed by the development of larger cranes which made use of human tread wheels. This made it possible for even heavier weights to be lifted (Matthies, Andrea 530)  Fig. 2 “Greco-Roman Pentaspastos, Five-pulley-crane” (Matthies, Andrea 529) Ancient Greeks discovered the crane above towards the end of the 6th century BC to assist them in raising heavy items. The pulley and winch replaced the ramps which were prevalent in use for lifting loads. This could only lift many small stones and not heavy ones. This was a set back in Greek technology but later on Greek construction engineers started using compound pulleys again (Lancaster 430) The heightened use of cranes in the ancient days was reached at the time of the Roman Empire. At this time there was a lot of construction work and buildings were being taken to higher heights. At that time the Romans took over the crane of the Greece and advanced on it.  Fig. 4 A treadwheel crane in use at Bonn in Germany (Matthies, Andrea 530) . The Roman crane trispastos which was the simplest was made of one beam jib, rope, and winch. It was also made of a block with three pulleys. Those cranes with the capacity to lift heavier loads were made of 5 pulleys. The largest of them had 3 sets with five pulleys in each set. They were made with 2, 3 or 4 masts. The number of masts was determined by the maximum load. The lifting capacity of Roman cranes is recorded to have been the highest compared to any other single crane (O’Connor, Colin 49). The High Middle Ages saw the reintroduction of the tread wheel crane which had been abandoned in Western Europe at the time of collapse of the Western Roman Empire. The earliest use of a tread wheel can be traced back to 1225 AD in France. The tread wheel was not in use in England before 1331. Harbor cranes are known to have been in use in 1244 in Utrecht, 1263 in Antwerp, 1288 in Brugge and 1291 in Hamburg. (Mathews, Michael 346).   Fig. 5 Double treadwheel crane; Available at: http en.wikipedia.org.wiki Cranes were more cheap and safe when used for lifting loads when compared to customary methods. Apart from the tread wheels cranes in the medieval times were powered by wind lasses which had radiating spokes. By the beginning of the 15th century they had windlasses resembling the wheels of a ship. To deal with impulse irregularities and to overcome dead spots while lifting loads fly wheels were being used from around 1123 (Coulton 10). The tread wheel used in the medieval ages was a big wheel made of wood with a central shaft on which the wheel turned. It also had a tread way with enough space for 2 workers. Earlier on the wheel called ‘compassion arm’ was made with spokes fixed into the central shaft. The later and more advanced ‘clasp arm’ model had arms in an arrangement like that of chords on the rim of a wheel. Consequently a thinner shaft was used which provided a bigger mechanical advantage (Lancaster 430)  Fig. 6 “Tower crane at the inland harbor of Trier from 1413” Medieval cranes were only used for vertical motion just like those used earlier in Rome and Greece. They were not useful in moving loads horizontally. Slewing cranes could permit for the rotation of loads but they were not in use until 1340. The cranes did not use brakes or ratchets to prevent the backward movement of the load. This absence was caused by a high force of friction present in the tread wheel of medieval times which reduced the possibility of the wheel accelerating at uncontrollable speeds (Daniel et al 30).  Fig. 7 A 1742, crane in Copenhagen, Denmark (Matthies, Andrea 525) “Stationary harbor cranes” were taken to be new technology for middle ages. The harbor crane had double trade wheels. It was used at the docks for lifting cargo on and from ships. Two types of this crane have been discovered to have existed in different geographical areas. In Denmark there were found gantry cranes which had a central vertical axle at the center as the pivot. At the German sea and the harbors within the inland there were found tower cranes (Coulton 10). In this tower cranes the windlass and the tread wheels were placed in a tower which had the room and the jib arm rotating. The Mediterranean region and Italy did not adopt the dock side cranes. They continued using the ramps even after the middle ages. To increase the loading speeds harbor cranes had double tread wheels. These wheels had a diameter of 4m or more. They had a capacity of between 2 and 3 tons which was the approximate weight of cargo at the ports. Alongside the stationary cranes there were other cranes called floating cranes that came in use in the 14th Century. They could be used in the entire port basin. In the early modern age Cranes were put to domestic use during the 17th to the 18th centuries. The chimney crane used at the fire place was important for swinging kettles and pots above the fire. A trammel was used to adjust the height at which the swinging was done (O’Connor, Colin 49). Conclusion The crane has been in use since the times of ancient Greek civilization. The original design of the crane was made of wood but later changed to cast iron or even steel at the time of the industrial revolution. Initially animals and manpower was the source of power for the cranes. With technological advancement the crane has been evolving from the Greek civilization to the Roman times to the middle ages to what it is now. Modern cranes use power from an internal combustion engine. Cranes are important for lifting heavy materials and are used in the construction industry, manufacturing and shipping industry. There are many other uses that cranes can be put to since they can in many types and every type has its own use. References Coulton, J. "Lifting in Early Greek Architecture", The Journal of Hellenic Studies 94: 1–19,  1974. Dienel, Hans-Liudger; Meighörner, Wolfgang. "Der Tretradkran", Publication of the Deutsches Museum (Technikgeschichte series) (München)  1997. Lancaster, Lynne. "Building Trajan's Column", American Journal of Archaeology 103 (3): 419–439  1999. Matheus, Michael.. Tradition und Innovation (4th ed.), Berlin: Gebr. Mann Verlag, pp. 345–348, 1996. Matthies, Andrea "Medieval Treadwheels. Artists' Views of Building Construction", Technology and Culture 33 (3): 510–547, 1992. O’Connor, Colin Roman Bridges, Cambridge University Press, pp. 47–51;1993. Read More